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Unread 08-16-2016, 12:28 PM
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Default Re: Vorshlag Ford Focus RS Development Thread

continued from above


Front tire wear after 83 street miles and 16 laps at MSR-C

This image above shows the total tire wear after our initial 16 lap track outing (two 8 lap sessions on a track surface with very low tire degradation), and the image below is after 2500 street miles 2 days of Todd racing at the Optima event. Overall the tires are wearing somewhat heavily BUT that's mostly due to the stock suspension losing so much camber in roll and too narrow of a tire for this car's weight. Overall this is about as good as we could expect for front tire wear on a 59% front heavy, effectively FWD, overtaxed and narrow tire that is losing 2-3 deg of camber when rolling in a corner.


Worn pretty poorly after 2 events but as good as we would expect considering the weight/size/suspension

To make this car faster in Optima competition - which includes autocross, speed stop, and time trial road course competition - there are several other settings we will alter to improve performance and tire wear. Then, once the tire killing suspension issues are improved we will ADD tire width, which should increase mechanical grip as well as deal with tire heat better from this car's weight and power level. Again, power has already increased by 10% (from 300 whp up to a dyno'd 330 whp after the COBB stage 1 tune). We explain the what and why we will change in the suspension below.

CAMBER SETTINGS MATTER AS MUCH OR MORE THAN PRESSURES


Track pictures make good data. This image is useful to tell us about camber settings, tire pressures and roll.

Tire pressures and camber settings are two of the most crucial settings a racer can alter to make the tires work more effectively, so we take these settings very seriously - we have to. We can only do so much with tire pressure changes, but a camber setting can make an even bigger improvement to tire performance and wear.

The ideal front camber setting for a modern radial tire will still have some visible negative camber when loaded fully in a corner. The Focus goes to about +2 positive camber under load, which is bad for both tire wear and ultimate grip - a significant portion of the loaded front tire isn't touching the ground. It is not "doing work".



Vorshlag is a multi-faceted business, but our primarily focus is to design and build suspension components to improve factory built cars for road course use. As suspension engineers and designers, our main goal when creating suspension components is simple: make the tires work more effectively. Everything we do with dampers, spring rates, adjustable camber plates, wheel widths, even chassis construction is done to optimize the tires when being driven on a road course or autocross conditions.

These 4 small contact patches of tire are the ONLY things connecting the car to the track surface, and we do everything we do to maximize the size of the contact patch (camber + tire pressure), and to make sure it isn't in the air (dampers + springs). "Tires in the air do no work" is a saying I use a lot, and if you look at slo-mo video of cars with poor dampers, the tires are not on the ground as much as you might think while cornering over even small track imperfects.



If you think about the pinnacle of motorsport - Formula1 race cars - they still use a LOT of static negative camber on their front wheels, which is visible in this Redbull F1 car above. Why is that? Don't these cars have the ultimate in suspension design? Ultra rigid carbon fiber control arms and carbon tubs that have zero deflection, metal suspension bushings that don't deflect? Double A-arm geometries that don't lose camber like a McPherson strut car does in roll? Super stiff spring rates, and THREE swaybars (front, rear, and FRIC) to control roll and heave? Yes, they have all of those things, and yet they still run -4 front camber, and on tighter street courses they run even more (Monaco). So it isn't unheard of for your Focus RS to need a lot more than the -1 it comes with from the factory. If we had the room we'd run the RS at -2.5 to -3 front camber on the otherwise stock suspension and tires.

On top of that, this RS is losing a lot of camber from roll and deflection (see below). One of the major problems we see in ALL late model, McPherson strut front suspension cars is a lack of camber control when loaded laterally in hard cornering. The front suspension bushings deflect and the soft springs roll so much that the car gets into a excessive roll condition. This makes the loaded outside tires start to roll off the ideal "flat" contact patch and onto the tire's shoulder.


This is not a tire/wheel position you ever want to see when cornering

The Focus is no different than almost any other "McStrut car" we have seen in the last 30 years - it loses a LOT of camber in roll due to several factors. A big part is the relatively soft set of springs and anti-roll bars used so that Granny Smith that buys one doesn't complain when she drives her RS down a dirt road to her farm house. Which means, in stock form, this car has a LOT of body roll. Next up is a big rubber bushing in the strut top mount, which deflects under lateral load, causing more camber loss at the tire. There are bushings on the lower control arm that also deflect under load (we will address this issue at a later date).


Left: Stock suspension too soft, lots of roll and camber going positive. Right: Much better with improved dampers, springs and camber

Here's a good side by side example. These two pictures above show McPherson Strut equipped S197 Mustangs in the same corner of the same race track (ECR Turn 11). We use this corner for a lot of testing because we can get great photos of cars here due to a placement of a flag stand nearby. The Mustang GT at left is bone stock (on 255mm street tires) and has a lot of roll and associated camber loss in the outside (left) front tire. The car on the right has a wider wheel and tire (295mm) yet has markedly LESS body roll and the loaded front tire still has negative camber when fully loaded. The car on the right has our fabricated Bilstein TrackPro kit coilover kit (a modified Bilstein inverted strut & shock) with 4 times the front spring rate and -3 of static negative camber. The lap times from this shock/spring/camber plate change were 4 seconds per lap quicker than when using the same 10" wide wheel and 295mm tire, and tire wear was greatly improved. It was 8 seconds per lap faster than on the stock suspension and stock tires. And EIGHT SECONDS is an eternity...


Even the $50K+ BMW 1M was very front camber limited in stock form - this tire damage happened in one HPDE weekend!

Changing to coilovers, quadrupling spring rates, and going to camber plates is a pretty drastic change just to keep the tire from shredding itself in a corner. Sometimes, like on this BMW 1M model (above and below), we can keep the stock sized tire from getting shredded on the outer shoulders just by adding a spherical top mount camber plate. We had enough room in the strut tower with the OEM springs/struts on these E82/E90 M models to do just that.


We fixed the 1M with camber-caster plates - more from negative camber dealt with the tire wear easily

These 1M could see as much as -1.7 camber in stock form, but that still wasn't enough when you factored in the rubber top mount deflection, soft springs, and associated body roll. The damage to the tires shown above was from 2 days on track at a normal HPDE weekend, when driven by an experienced road racer pushing the car 10/10ths. With our spherical camber plates the camber adjustment went to over -2.8 while keeping the stock springs (they can get more camber with smaller diameter coilover springs). This small change - just one degree more negative camber and less deflection from changing out the rubber strut top mount - allowed this 1M and many more to stop killing front tires in one weekend.



We have do this "camber fix" on dozens of McStrut cars and hoped to do the same on the Focus. As my Focus Suspension Challenges video from last time showed, there is just not enough room to move the OEM front spring inboard before it hits the tower, so we have to change to coilover springs and new struts to allow for this much needed camber adjustment. That happens this week!

TIRE WIDTH PER UNIT WEIGHT RATIO

Another factor (other than the soft suspension) that is hurting the Focus on track, for both ultimate grip and especially long term tire wear, is the relatively narrow tire it comes with. The 235mm tire coupled with the 3450 pound as tested weight makes for a difficult "tire width per unit weight" ratio for the RS to overcome - and is another item we will address to try to lower lap times on this car. So many magazine writers fixate on power-to-weight ratios, but almost nobody ever talks about tire-width-to-weight ratios. Which, for handling, is so much more important than power!


Jarrett Jan's 2235 pound Miata on 225mm tires has more equivalent tire than our 3600 pound Mustang on 335mm tires?!

Some friends and I that autocrossed back in the 1980s-90s figured this out early on. We used to keep track of weights and tire widths use when comparing autocross times - because it was alarming how well CRX and Miata models did on slower courses on their "smaller tires" compared to more more powerful yet heavier cars we tended to race with. The truth was that these little/light cars had a HUGE tire-per-unit-weight advantage. Here's a quick calculation for the 2 cars above: a 2250 pound NA Miata on a 225 tire would equate to a 3600 pound Mustang needing a 362mm of tire for an equivalent weight to tire width! Even with the 335mm tires we ran at Optima events (above right) we were at a distinct disadvantage to this Miata on the same model and compound 225mm tire.



Let's do a comparison that isn't fair, yet is still valid. A C6Z06 Corvette with 505 hp weighs 3217 in this version (2012 model with factory optional 20" wheels). This is a big car, with 51%F/49%R weight bias has OEM 335mm width tires on a 20x12" rear wheel (which weighs 8 pounds more than the Focus 19x8" wheel and 235mm tire). This is the rear drive wheels so they are critical on track. The Focus at 3445 pounds on a 235mm tire is at a huge tire-per-unit-weight ratio disadvantage.

To have an equivalent tire as the C6 Z06, the Focus RS would need to to be running a 358mm wide tire. Of course there are other variables at play, and the AWD system of the Focus should close some of that "tire advantage" gap in slow speed corners (autocross), but as we've seen the AWD advantage has almost no effect on a proper road course - unless it is raining, there are VERY slow corners, or the Focus gained another ~200 whp. Once you get off the super narrow OEM tires, we have found that AWD doesn't do almost anything on a lower powered car above certain speeds.

We have noted this in NASA Time Trial racing - once the cars are built to the limit of a power-to-weight ratio class, and tire sizes are no longer restricting the car, the AWD cars lose their advantages. They just... don't win many more events than 2WD cars. AWD really shines in dirt/gravel/snow, of course, but we don't road race on courses with much dirt, gravel or snow.

THE "FAIR" FOCUS RS TO EVO X COMPARISON


Bone stock 2008 Mitsubishi EVO X MR - with sticker power!

I want to get back to the EVO X for a minute - a car I compared the Focus RS to in my first two posts in this thread. This was a car that was very similar to the Focus RS in many ways, which we worked with over 2 years and made much better, and won a lot of autocross and time trial events in - a 2008 EVO X MR. It also had a few notable differences, but overall they were more similar than not.


Left: Inverted monotube Bilsteins on the MR were better, but springs were too soft. Right: Factory 18x8.5" and 245mm tire = 46.8 pounds

The EVO X was a $35,000, relatively heavy 4 door AWD car with a front weight bias - all similar to the RS. It has a turbo and intercooled 2.0L engine, beefy Brembo brakes (with 2-piece rotors), factory launch control (really a 2 step rev limiter, just like the RS), and rode on relatively soft stock suspension. The MR came with a slightly better shocks (inverted Bilstein struts, which have less strut deflection when loaded than a twin tube strut), the dual sequential transaxle (so nice, when it worked), and a more sophisticated rear suspension. It had a 245mm tire on a 18x8.5" wheel, so a very similar stock tire-to-weight ratio to the RS. It made 300 hp in stock form but with exhaust changes and a tune we got it to over 380 whp, which some are already able to get to in a modified RS.



I went back and read our EVO X development thread and I noted that we wrote that it suffered from similar "stock suspension" challenges, which are visible in the track and autocross images shown when raced it on the stock suspension, after initially upgrading to a slightly more competitive 245mm Dunlop tire on the stock 18x8.5" wheels. The car had a TON of body roll, front camber loss, and brake dive in this "stock suspension" autocross I raced it in, shown above. About the same as the Focus has, in all fairness.



In stock form it was pretty terrible, so maybe I was too harsh on the RS? If so, here is my apology to Ford and the RS' fans... the EVO X was equally as crappy as the RS. It just seemed like the RS had so much positive press and hype you'd think it was a space ship - but the EVO X was treated much the same way by car mags and forum fan boys alike.



We didn't keep the EVO X on the stock suspension very long, and after one autocross and one NASA Time Trial it got coilovers and camber plates. I was just remembering how much better it was the majority of the time we used this car over 2 seasons - with properly upgraded suspension.

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